Cold sores, also called fever blister or Herpes simplex, are groups of fluid- filled blisters. They often erupt around the lips or sometimes under the nose or around the chin. Cold sores caused by herpes virus type 1 are very contagious. The initial infection (primary herpes), which often occurs before adulthood, may be confused with a cold or flu and can cause painful lesions to erupt throughout the mouth. 

Once a person is infected with primary herpes, the virus stays in the body and causes occasional attacks. For some people, the virus remains inactive, recurring herpes lesions look like multiple tiny fluid-filled blisters (cold sores) that most commonly appear around the edge of the lips. An attack may follow a fever, sunburn, skin abrasions or emotional upsets.

Treating cold sores 

Cold sore blisters usually heal in a week by themselves. Over-the-counter topical anesthetics can provide some relief. Prescription antiviral drug may reduce these kinds of viral infections.